FIGURE 5.6 Models of the response between arbuscular mycorrhizal plants to mycorrhizal infection and soil phosphorus availability. Graph a depicts each plant species in the community responding in the same way, with a reduction of mycorrhizal colonization of roots with increasing P supply. In this situation, the net ecosystem effect is for a general reduction in mycorrhizal associations. Graph b depicts a variable response of each plant species in the community, resulting in a net lack of mycorrhizal response throughout the ecosystem. Source: From Allison and Goldberg (2002).

ABSTRACT

The influence of mycorrhizae on plant performance is influenced by edaphic controls exerted by changes in soil chemistry. Bever et al. (1997) developed a model to explain the importance of feedback mechanisms between the soil community and plant

population dynamics. Using mixtures of four plant species, they demonstrated that growth could be enhanced or inhibited by soils in which the same or different plant species had been previously grown (Fig. 5.7). They suggest that changes in the soil organisms and nutrients or plant-antagonistic chemicals can act in either a positive or negative feedback mechanism to affect growth of subsequently planted species. Similar changes in plant fitness can be related to small-scale in soil nutrient availability heterogeneity. Farley and Fitter (1999) showed that root proliferation of seven

co-occurring woodland plant species responded differently to localized nutrient-rich patches in soil. This difference in response was not affected by mycorrhizal status, but the differential growth response led to an improved level of competition by the plant species that responded by producing more root biomass.